The present application claims priority to German application 100 19 554.7 filed on Apr. 18, 2000, the subject matter of which is hereby incorporated by reference.
The present invention relates to mixtures of at least one filler and organosilicon compound, and to a process for their preparation and use.
It is known that hydrolysable organofunctionalised silanes which are capable of reacting with fillers containing hydroxyl groups, such as, for example, natural and synthetic silicates, carbonates, glasses and metal oxides, are used in many fields of application for surface modification or for adhesion promotion. A number of such organofunctionalised silanes are used in rubber technology as adhesion promoters between filler and rubber (EP 501 227; Gummi, Fasem, Kunststoffe 51:416-424 (1998)). This is especially true of sulfur-containing alkoxysilanes of the general formula Yxe2x80x94Sx-Z, wherein Y is R1R2R3Sixe2x80x94R4, in which R1, R2, R3 may be identical or independent of one another a C1 to C4 alky or a C1 to C4 alkoxy; R4 may be a C1, to C6 linear or branched alkylidene; x is a number from 1 to 10; and Z is H, CN or, preferably, Y,
It is also known that hydrolysable organofunctionalised silanes condense in the presence of liquid or surface-bonded water to form high molecular weight polysiloxanes. As a result, they may lose at least some of their activity, which is not acceptable from a technical or economical point of view (Silane Coupling Agents, sec. ed. Edwin P. Plueddemann, Plenum Press). In addition, such organofunctional silanes are mostly liquids and therefore frequently more difficult to handle in terms of processing technology than solid, pourable products.
Organofunctional silanes are also offered for sale and employed, especially for rubber technology, in the form of solid mixtures fixed to a carrier. Porous solids having a high absorptive capacity are predominantly used as carrier material. These carriers are used to absorb as much liquid silane as possible, do not to enter into a reaction with or promote a polycondensation reaction of the silane, and release the silane again completely and as quickly as possible during processing. In addition, the carrier material remaining in the product must not lead to an impairment of the properties of the product.
It is clear that good storage stability of the mixture is ensured when the carrier does not contain any moisture and/or surface-functional groups that are able to react with the organofunctional silane. A large number of different materials are being investigated for use as carriers, such as industrial carbon blacks, waxes, chalks, kaolins and natural or synthetic silicas. The various carrier materials differ not only in their absorptive capacity but also in their inertness towards the silane.
Mixing silanes with carbon black has proven to be advantageous in rubber technology with respect to adsorptive capacity, pourability and storage stability (DE 27 47 277). Organosilicon mixtures with white, untreated mineral carriers are disclosed in DE 22 55 577. WO 97/07165 describes organosilicon mixtures with dried silica as the carrier, such mixtures having to be stored in closed containers in order to minimize condensation. In the case of a product according to DE 22 55 577, a storage stability of only 3 months is guaranteed owing to its susceptibility to hydrolysis (product information reinforcing additive Si 69, X 50-S, X 50, Degussa AG).
Disadvantages asssociated with past silanes include the black colour of mixtures with carbon black (DE 27 47 277), which rules out use for colored products, poor storage stability (DE 22 55 577, WO 97/07165) owing to the moisture that is always present and reactive hydroxyl groups, and the low adsorptive capacity of wax.
The object of the invention is to provide a white organosilicon mixture that has improved storage stability.
The invention provides a mixture of at least one filler and organosilicon compound of the general formula Yxe2x80x94Sx-Z, wherein Y=R1R2R3Sixe2x80x94R4xe2x80x94 and R1, R2, R3 may be identical or different and represent a C1 to C4 alkyl or a C1 to C4 alkoxy, R4 represents a linear or branched alkylidene having from 0 to 6 carbon atoms, preferably from 2 to 4 carbon atoms, x is a number from 1 to 10, preferably from 2 to 5, and Z represents H, CN or Y, characterized in that the filler is surface-treated, hydrophobic, precipitated silica.
There may preferably be used organosilicon compounds of the formula Yxe2x80x94Sx-Z wherein Y=R1R2R3Sixe2x80x94R4xe2x80x94 and R1, R2, R3 =methoxy or ethoxy, R4 =CH2CH2CH2, x is a number from 1 to 10, and Z represents H, CN or Y. Special preference is given to the use of organosilicon compounds of the formula (C2H5O)3Sixe2x80x94(CH2)3xe2x80x94Sxxe2x80x94(CH2)3xe2x80x94Si(OC2H5)3, . . . where x is a number from 1 to 10. The content of organosilicon compounds may be from 30 to 70 wt. %, preferably from 40 to 60 wt. %, based on the mixture.
The surface-treated, hydrophobic, precipitated silica may have a BET surface area of from 50 to 200 m2/g, preferably from 80 to 120 m2/g, a DBP adsorption of from 200 to 350 g/100 g, preferably from 210 to 250 g/100 g, and a moisture content of from 2 to 6%, preferably from 2.5 to 3.5%. Surface-treated, hydrophobic, precipitated silicas are known, for example, from DE 1 172 245 and DE 25 13 608 and are distinguished by an extremely low hydrodroxyl group density, low methanol wettability and a low moisture content. The high degree of hydrophobicity of the silica allows it to be used as a carrier material for the above-described hydrolysis-sensitive organosilanes. There may preferably be used the two hydrophobic silicas Sipemat D10 and Sipemat D17 from Degussa-Hxc3xcls AG.
The invention relates also to the preparation of the mixtures described above, in which the organosilicon compound is homogeneously applied from a nozzle to the surface-treated, hydrophobic, precipitated silica in a mixing unit at temperatures  less than 50xc2x0 C. The preparation of the mixture is generally complete after a short time. Trough-shaped powder mixers having a rotating propeller tool may be used as mixing units.
The mixture according to the invention may be used in rubber compositions. The mixtures may be added to the rubber composition in such an amount that from 0.1 to 50 wt. %, preferably from 0.1 to 20 wt. %, of organosilicon compound, based on the amount of rubber filler used, is added. The rubber compositions may contain at least one synthetic rubber and/or natural rubber and at least one silica and/or carbon black as rubber filler. Preferred synthetic rubbers are described, for example, in W. Hoffmann, Kautschuktechnologie, Genter Verlag, Stuttgart 1980 and may be polybutadiene (BR), polyisoprene (IR), solution/emulsion styrene/butadiene copolymers having styrene contents of from 1 to 60 wt. %, preferably from 5 to 50 wt. % (SBR), isobutylene/isoprene copolymers (IIR), butadiene/acrylonitrile copolymers having acrylonitrile contents of from 5 to 60 wt. %, preferably from 10 to 50 wt. % (NBR), partially hydrogenated or completely hydrogenated NBR rubber (HNBR), ethylene/propylene/diene copolymers (EPDM), as well as mixtures of those rubbers.
The rubber compositions may also contain rubber auxiliaries, such as, inter alia, reaction accelerators, reaction retardants, anti-ageing agents, stabilizers, processing auxiliaries, plasticizer, waxes, metal oxides as well as activators, such as triethanolamine, polyethylene glycol, and hexanetriol.
The rubber auxiliaries are used in conventional amounts, which are dependent inter alia on the intended use. Conventional amounts are, for example, amounts of from 0.1 to 50 wt. %, based on rubber. The organosilanes of the general structure Yxe2x80x94Sx-Z may be used alone as the cross linking agent. Generally, however, it is recommended to add at least one further cross linking agent. Sulfur or peroxides may be used as further cross linking agents. The rubber mixtures according to the invention may also contain vulcanization accelerators. Examples of suitable vulcanization accelerators are mercaptobenzthiazoles, sulfenamides, guanidines, thiurams, dithiocarbamates, thioureas and thiocarbonates. The vulcanization accelerators and sulfur or peroxides are used in amounts of from 0.1 to 10 wt. %, preferably from 0.1 to 5 wt. %, based on rubber.
Vulcanization of the rubber mixtures may take place at temperatures of from 80 to 200xc2x0 C., preferably from 130 to 180xc2x0 C., optionally under pressure of from 10 to 200 bar. The preparation of the rubber mixture may be carried out in conventional mixing units, such as rollers, internal mixers and mixing extruders.
The mixture according to the invention may be used in the production of molded bodies, especially tires, tire treads, cable coverings, hoses, drive belts, conveyor belts, roller coverings, shoe soles, gaskets, profile sections and damping elements.